The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Optical disk drives use laser technology to store data on optical storage media, generally referred to as digital versatile disks (DVD's). Data is stored on DVD's in tracks having spiral paths. FIG. 1A shows a track 10 having a spiral path 12. The spiral path 12 of the track 10, however, is not perfectly spiral in shape. Instead, as shown in FIG. 1B, the spiral path 12 of the track 10 wobbles around an average centerline 14 of the spiral path 12 like a sinusoid 16.
Sinusoidal deviation of the track 10 from the average centerline 14 of the spiral path 12 of the track 10 is called a wobble. Phase-modulated data embedded in the wobble provides location information for the track 10. A wobble signal provides a measure of the sinusoidal deviation (i.e., the wobble) of the track 10.
When writing data on the track 10, a recorder follows the track 10 and locks a timing loop to the wobble signal of the track 10. The recorder uses the location information of the track 10 that is embedded in the wobble signal of the track 10 to align the writing apparatus to the track 10.
The storage capacity of a DVD depends on the diameter of the DVD and the recording format used to record data on the DVD. DVD's are generally 80 mm or 120 mm in diameter. The 80 mm DVD's typically store 1.46 GB of data per side. The 120 mm DVD's typically store 4.7 GB of data per side.
The recording formats used to record data on DVD's are standardized by European Computer Manufacturers Association (ECMA). For example, the ECMA-337 standard, which is incorporated herein by reference in its entirety, defines data interchange on 80 mm and 120 mm DVD's using +RW format at recording speeds of up to 4×. The ECMA-349 standard, which is incorporated herein by reference in its entirety, defines data interchange on 80 mm and 120 mm DVD's using +R format at recording speeds of up to 8×.
Additionally, DVD's can be recordable or re-writable. Data can be written only once on recordable DVD's. Thereafter, the recordable DVD's are read-only, and data cannot be written again on recordable DVD's. Therefore, recordable DVD's are also called read-only DVD's and are referred to as DVD+/-R. The letter “R” denotes recordable DVD's. The ECMA-359 standard, which is incorporated herein by reference in its entirety, defines characteristics of recordable DVD's. On the other hand, re-writable DVD's are re-recordable. That is, data can be written again on re-writable DVD's. In other words, data can be recorded on re-writable DVD's more than once. Therefore, re-writable DVD's are referred to as DVD+/-RW. The letters “RW” denote re-writable DVD's. The ECMA-338 standard, which is incorporated herein by reference in its entirety, defines characteristics of re-writable DVD's. Thus, DVD-R and DVD-RW that are 80 mm in diameter can store up to 1.46 GB of data per side. DVD-R and DVD-RW that are 120 mm in diameter can store up to 4.7 GB of data per side.